When performing, for example, therapy, examination, and the like by inserting a medical device such as a catheter or the like, into a blood vessel, in general, an introducer sheath is indwelled in a blood vessel by puncturing the skin to the blood vessel to insert the medical device into the blood vessel through the introducer sheath. However, when using such an introducer sheath, it is necessary to bore or form a large hole in the skin up to a blood vessel to accommodate a portion of the introducer sheath, and therefore, a burden on a patient increases.
In Japanese Application Publication No. 2012-85816, a catheter assembly which is designed to insert a catheter into a blood vessel without using an introducer sheath is proposed. In the catheter assembly, a dilator is inserted into the catheter which is introduced into a blood vessel in a state where the dilator protrudes from a distal portion of the catheter. The size of the puncture hole decreases as much as the portion in which the introducer sheath is not used, and therefore, it is possible to reduce a burden on a patient during puncturing.